Fix .android_secure backup... again

There was actually a bug in TWRP that was making this a headache. This
has been resolved so we can return to the more natural /sdcard path for
internal storage.

Change-Id: Ibd51de147e715f3733990a00ed4a9887265f4ecd
Disable legacy property system

Change-Id: I886fda9b208d53a5593a9d5f5890b1f0678a1b4f
Support /data/media partition layout

Change-Id: Ifd282d760b0feaf4a9e45f19b4feae46a999f94c